DNS Propagation Delay Explained

Whenever you change/update the IP or name servers of a domain name, You might have heard this term “DNS propagation delay” from hosting providers. Every domain undergoes this “DNS propagation delay” during the initial stages of it’s set up. This article describes the DNS propagation delay and how to Speed Up the DNS Propagation.

DNS:

Domain Name System in short DNS, is the service which translates that domain name you type into your browser into an IP address, and tells your browser, which server it needs to connect to load the site.

How DNS works:

When your website’s address is entered into a browser, the computer requests the IP address of the server hosting your site from your Internet Server Providers (ISP) DNS records. If the site is not listed in the records it queries registrars to find out who the DNS start of authority (SOA) is for your website. If you’re using your registrar’s name server as your SOA, it looks up the “A” record for your domain and returns the IP address of the server listed. If you are using our name servers, the registrar points the browser to our DNS servers to determine the IP Address for your domain name. From there the request is sent to the server the domain is hosted on which then provides the browser with the website.

Propagation Delay:

To speed up the above mentioned process, Internet Service Providers (ISP) caches their DNS records. They create their own copy of the master record, and access it locally to search for website, each time someone tries to view it. This procedure speeds up the internet, reduces the traffic and thus help ISP work faster. Each ISP caches DNS record and update it only every few days, any changes you make to your DNS records are not reflected between those updates. Each ISP have there own standard time frame to update the cache DNS record. This delay from your ISP will prevent you from viewing your website. This process is known as DNS propagation delay. The slow updating of the server cache is called propagation.

Benefits of caching DNS at ISPs

1. This will decrease the return time it takes for a web browser to request a domain lookup to get the IP address.

2. Reduce the web-traffic

Why its taking too long to propagate:

We are now familiar with the term Propagation Delay, it will be a bottleneck when you change the IP/nameservers of a live website. As we all know this delay is due to the caching of DNS values at ISPs. The time for which these values remain in cache is controlled by the TTL (Time to Live) value set in the resource DNS records. For example, if the A record of the site has a TTL value, say 14400 seconds (4 hours), then this result will stay in the DNS cache for 4 hours once fetched from the authoritative name servers. If the IP address of this site is changed in between, the name server which caches the previous result will not be able to see this change as it is still fetching the details from it’s local cache.

How to reduce the propagation delay

As we mentioned the time for the DNS values remain in cache is controlled by the TTL, So, to reduce the delay due to DNS caching, we need to reduce the TTL value in resource records. We will explain how to change the IP of a domain with less downtime/propagation.

We assume current TTL vale is 14400 seconds (4 hours)

1. Change the TTL value to 300 seconds and wait for 14400 seconds for the new TTL value to be effective.

2.Change the IP address of site. This new IP address will be propagated on Internet within 5 minutes (300 seconds) as name servers will cache the result only for 5 minutes.

3.Once the IP address is changed and site is accessible, you may change the TTL value back to 14400 seconds. This will help to reduce the DNS queries on the authoritative name servers and will speed up loading the website.

There are some useful online tools to check the DNS propagation.

Whatsmydns will check the propagation with a common set of name servers around the globe, and tell you whether or not certain records related to your website have propagated to them.

Intodns will provide you a complete list of your DNS records if available.

If the site is not loading even after 48 hours and the above two sites do not show the DNS records available, there might be issues with your DNS configuration, contact our support department for further checking.